A professional diagramming tool that helps users visualize complex information through easy-to-understand diagrams.
Douglas,
The good news these days is that you don't even need a viewer. If your Visio diagrams are stored in OneDrive for Business or SharePoint Online, they can be viewed in Safari on a Mac, iPhone, or iPad and they will look exactly as they do in a browser on a PC.
It is truly any browser on any device and a Visio license is not required. Viewing in a browser even allows people to add comments to the diagram and a license is still not required. This article includes a few more details.